Once a well has been drilled, cased and cemented, hydraulic fracturing turns it into a producer. The job is broken into discrete stages spaced along the horizontal lateral. Each stage treats a short section of the wellbore, and the crew works through them in sequence — typically from the far end of the lateral (the toe) back toward the vertical section (the heel).
The frac sequence, stage by stage
Within a single stage, the operation follows a repeatable cycle:
- Perforate. A perforating gun is run in on wireline and fired, punching holes through the casing and cement into the target rock so fluid can reach the formation.
- Pump frac fluid. Fluid is pumped at high pressure until the rock cracks and the fractures grow.
- Place proppant. A proppant-laden slurry is pumped so the sand or ceramic is carried into the open fractures.
- Release pressure. Pumping stops and pressure is bled off. The fractures try to close, but the proppant wedges them open, preserving the flow paths.
- Isolate and advance. The completed stage is isolated and the crew moves to the next interval up the lateral.
Modern horizontal wells are commonly fractured in 30 to 60 or more stages. Treating the lateral in many short stages places proppant more evenly and contacts far more reservoir rock than a single large treatment ever could.
Why stages matter
Pumping one giant treatment along an entire two-mile lateral would waste energy on the easiest-to-break rock and starve the rest. Splitting the lateral into many isolated stages lets the crew direct full pump pressure at one short interval at a time, fracturing it thoroughly before isolating it and moving on. The result is a denser, more uniform fracture network and much higher recovery.
The two dominant ways to isolate stages are plug-and-perf and sliding-sleeve systems. Plug-and-perf uses wireline-set frac plugs and perforating guns and is the most widely used method in cased-hole completions. Sliding-sleeve systems use pre-installed sleeves opened by dropped balls or pressure, allowing many stages to be treated in a single continuous pumping session.
After the frac
When all stages are complete, any frac plugs left in the casing are drilled or milled out so the entire lateral is open to flow. The well is then flowed back to recover load fluid, and production tubing and surface equipment are installed so the well can begin producing oil and gas.
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Frequently asked
It varies with the number of stages and operation, but multi-stage fracs on a horizontal well typically run over a period of days to a couple of weeks, with several stages treated per day.
The toe is the far end of the horizontal lateral, deepest into the formation; the heel is where the wellbore curves from vertical to horizontal. Fracking generally proceeds from the toe back to the heel.
Frac plugs isolate each stage during treatment. Once all stages are fractured, the plugs are milled out so the full length of the lateral is connected to the wellbore and can produce.